摘要:

With the advent of the “green” revolution, the semiconductor industry must develop alternative processes that utilize environmentally friendly products. As a first step toward this end we have demonstrated an electron beam patterned sub-quarter micron T-gate process using safe resists manufactured by Microlithography Chemical Corp. (MCC). Instead of the more conventional chlorobenzene based poly methyl methacrylate (PMMA) and 2-ethoxyethanol copolymer solutions, new anisole based PMMA and an ethyl lactate based copolymer are used. In addition to replacing the non-environmentally friendly resists, we sought to increase gate yield by improving the shape of the resist profile. Focused ion beam (FIB) cross-sectional analysis of 0.2 μm T-gates fabricated using our conventional process showed metal discontinuity at the stem-to-cap transition. This was attributed to a sharp transition in the resist from the bottom layer of PMMA to the copolymer. With the safe resists we sought to grade the transition between the stem and cap to improve metal continuity. Multiple techniques were used to evaluate and characterize the safe resist process. FIB cross sectioning provided a rapid and less destructive method for resist profile inspection. In addition, metal deposition was examined prior to liftoff to view evaporation buildup. Scanning electron microscopy and atomic force microscopy were used to give comparative measures of gate length. A safe resist process for sub-quarter micron T-gate fabrication is described.

ISSN:1071-1023    

DOI:10.1116/1.589754

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

The masking properties of nanometer scale polymethylmethacrylate (PMMA) features used for definition of sub-100-nm-wide bridges inInP/Ga0.25In0.75Astwo-dimensional electron gas heterostructures by wet etching were investigated. Bridges untreated after the development of PMMA showed very poor masking ability due to a substantial exposure by backward scattered electrons from the surrounding exposed areas. However, if the resist was post-baked after development at a temperature higher than the glass transition temperature,Tg,the masking properties were restored and wet etched nanobridges of a sufficient quality were obtained. The post-development bake temperature and time were optimized to provide enough resist “packing” and yet not to cause resist flowing resulting in unacceptable alteration of the pattern geometry.

ISSN:1071-1023    

DOI:10.1116/1.589755

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

Ligand stabilized metal clusters are becoming of considerable interest for possible nanoscale electronics applications. In this article, we report the fabrication and near-room temperature electrical transport properties of structures made from the gold-cluster materialAu55[P(C6H5)3]12Cl6.While other strategies to produce cluster arrays have been reported, this work is the first to use electron-beam lithography to laterally define the structures. We compare the current–voltage characteristics of nonpatterned and patterned structures, and show that in both cases the nonlinear behavior observed is consistent with Coulomb blockade dominated transport. We argue that charging of individualAu55cores is responsible for the effects observed.

ISSN:1071-1023    

DOI:10.1116/1.589756

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

Effect of the regrowth temperature of the cap layer grown successively on a Si focused ion beam (FIB) implanted GaAs surface on the dopant activation was investigated using a FIB/molecular beam epitaxy combined system. Indication of the reevaporation of the implanted Si was observed at high regrowth temperature and the fabrication process was improved by using low regrowth temperature. A high doping efficiency was obtained for the ion dose at about1×1013 cm−2.Present results indicate the importance of controlling the regrowth condition to obtain high doping efficiency.

ISSN:1071-1023    

DOI:10.1116/1.589757

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

In this article we describe a method for direct epitaxial growth of thin-film structures using a combination of resistless electron beam lithography and supersonic molecular beam epitaxy. Electron beam irradiation of a surface hydride layer on silicon induces hydrogen desorption and hence alters the surface reactivity of the exposed area. Introduction of a source gas concurrently with, or immediately following electron beam exposure results in a pattern formation on the exposed area. Continuous silicon oxide patterns with linewidths below 0.1 μm have been achieved. The resulting pattern can be also used as a mask for subsequent selective growth on the unexposed area. Supersonic molecular beam epitaxy is a highly nonequilibrium film growth method that uses translationally hot source gas species generated by a high pressure gas expansion. Since the reactivity of the source gas molecules depends exponentially on the incident kinetic energy, the chemical selectivity of the film growth process can be altered by tuning the incident kinetic energy. Arbitrary patterns with linewidths on the order of 0.1 μm have been achieved with Si, Ge, and SiC epitaxy on Si (100) and Si epitaxy on Ge (100).

ISSN:1071-1023    

DOI:10.1116/1.589758

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

Blazed, grazing incidence x-ray reflection gratings are an important component of modern high resolution spectrometers and related x-ray optics. These have traditionally been fabricated by diamond scribing in a ruling engine, or more recently by interferometric lithography followed by ion etching. These traditional methods result in gratings which suffer from a number of deficiencies, including high surface roughness and poor control of the groove profile. These deficiencies lead to poor diffraction efficiency and high levels of scattered light. We have developed a novel fabrication method for fabricating blazed x-ray reflection gratings which utilizes silicon wafers that are cut 0.7° off of the (111) plane. In solutions such as potassium hydroxide (KOH), silicon is etched in 〈111〉 directions orders of magnitude slower than in other directions, resulting in extremely smooth {111} facets. The gratings are patterned using interferometric lithography with 351.1 nm wavelength and transferred into the substrate using tri-level resist processing, reactive-ion etching (RIE), and silicon nitride masking during the KOH etch. The narrow(<0.1 μm)ridge of silicon which supports the nitride mask is removed using a chromium lift-off step followed by aCF4RIE trench etch. The result is a grating with extremely smooth blaze facets which is suitable for x-ray reflection after evaporative coating with thin Cr/Au. Atomic force microscope images confirm that fabricated gratings have less than a 0.4 nm rms roughness—much smoother than conventional gratings which have over∼1 nmroughness. Theory predicts that reduced blaze facet roughness increases diffraction efficiency. Experiments and simulations performed at the Lawrence Berkeley Laboratory and Columbia University confirm that efficiency is increased; in fact, measured peak efficiencies reach∼80%of calculated theoretical limits. Peak grating efficiencies were achieved that are∼35%greater than that of the best available ruled masters of comparable design.

ISSN:1071-1023    

DOI:10.1116/1.589759

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

We describe the nanofabrication of subwavelength, binary lenses in GaAs for operation in the infrared. Subwavelength surface relief structures create an artificial material with an effective index of refraction determined by the fill factor of the binary pattern and can be designed to yield high-efficiency diffractive optical elements. In this work, we designed and fabricated a circular-aperture, off-axis lens with a deflection angle of 20°, focal length of 110 μm, and diameter of 80 μm, for operation at 975 nm. The off-axis lens design has a theoretical efficiency of 92% and the fabricated lens exhibits a diffraction efficiency into the first order of 72% and 59% of the transmitted power for TE and TM polarization, respectively. A significant advantage of these subwavelength structures is that fabrication requires only a single-lithography-and-etch-step process, in this case, electron-beam lithography and reactive-ion-beam etching.

ISSN:1071-1023    

DOI:10.1116/1.589760

出版商:American Vacuum Society    

年代:1997

数据来源: AIP